Palm oil recirculating system for cold-strip mill

ABSTRACT

A system of recirculating lubricant palm oil in a cold-strip mill, including an iron remover for separating iron from used palm oil by using sulfuric acid and steam available in the mill, which steam provides heat and agitation for separating the iron as iron sulfates. The system also removes fatty acids in the used plam oil by saponifying them, so as to recirculate iron-free and fatty-acid-free palm oil to the cold-strip-mill.

United States Patent [191 Tanaka et al.

[ June 18, 1974 PALM OIL RECIRCULATING SYSTEM FOR COLD-STRIP MILL [75]Inventors: Takayoshi Tanaka, Narashino;

Mitsukane Nonoyama, Chiba, both of Japan Kawasaki Steel Corporation,Kobe City, Japan 221' Filed: Apr. 23, 1973 21 Appl. No.: 353,560

[73] Assignee:

Foreign Application Priority Data [52] US. Cl 210/177, 210/168, 423/138[5]] Int. Cl B0ld 35/18 [58] Field of Search 210/177, 178, 168;

[56] References Cited UNITED STATES PATENTS Vinson 2l0/l77 X 3/1957Parsons 210/177 X Primary Examiner-Granville Y. Custer, Jr. AssistantExaminer-r-DeWalden W. Jones [5 7] ABSTRACT A system of recirculatinglubricant palm oil in a coldstrip mill, including an iron remover forseparating iron from used palm oil by using sulfuric acid and steamavailable in the mill, which steam provides heat and agitation forseparating the iron as iron sulfates. The system also removes fattyacids in the used plam oil by saponifying them, so as to recirculateiron-free and fatty-acid-free palm oil to the cold-strip-mill.

7 Claims, 7 Drawing Figures From steel/nil! PATENIEUJUN 1 81974 SHEU 20F 7 5 l0 Rate of adding sulfuric acid by volume) 2 m \IQX E 59. B

Pmwnmummu 3317384 satin or 7 EI S Q LE /000- 0 5 10' Rare of addingsulfuric acid byva/ume) PMENTEHM 1 8 m4- .sum 5 m7 lb 2b Hearing time(min) PM WWW 14 33-17384 'SHEEH'UFT I20 Standing time (min) PALM OILRECIRCULATING SYSTEM FOR COLD-STRIP MILL BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to a system ofrecirculating palm oil in a cold-strip mill, and more particularly to asystem for collecting waste palm oil and recovering reasonably pure palmoil for reuse in the cold-strip mill.

2. Description of the Prior Art Palm oil has been used as a lubricant incold-strip mill for making steel sheets, together with cooling water.The lubricating palm oil is collected together with cooling water in anoil cellar after being used, and the palm oil and water thus collectedare discarded as waste despite the fact that they still contain aconsiderably large amount of useful ingredients. Since a sizeable amountof palm oil is used in a modern cold-strip mill, such discarding of palmoil may cause an environmental pollution problem.

To mitigate such difficulty, it has been proposed to regenerate orrecover palm oil from the waste in the oil cellar. Because of the largeamount of palm oil to be handled, the conventional palm oil recoveringprocess has been costly. With one of known recovering processes, themixture of the used palm oil and the cooling water from the oil cellaris brought to a skimming tank for standing there for the purpose ofseparation of the palm oil from the water. The palm oil thus separatedin the skimming tank is further treated by a centrifugal separator forremoving impurities therefrom. The palm oil from the centrifugalseparator is used again in the cold-strip mill for lubrication. Suchconventional palm oil recovering process has a number of shortcomings:namely, that the cooling water from the skimming tank contains acomparatively large amount of palm oil, and that the centrifugalseparator cannot effectively remove impurities, such as iron particles,oxides of iron, and iron salts of fatty acid, so that such impuritiescause plugging of palm oil injection nozzles at the cold-strip mill. Theplugging of the nozzles inevitably results in degradation of steelsheets which are made by the coldstrip mill.

Therefore, an object of the present invention is to obviate theaforesaid difficulties of conventional palm oil recirculating process ina cold-strip mill, by providing an improved system for recoveringreasonably pure palm oil for recirculation.

SUMMARY OF THE INVENTION A mixture of lubricating palm oil and coolingwater from a cold-strip mill is brought into a skimming tank forseparating palm oil from the water. The palm oil thus separated at theskimming tank is chemically treated for removal of iron and iron oxidesby adding sulfuric acid therein, decomposing iron salts of fatty acidfor removal of iron by the sulfuric acid thus added, removing sulfatesthus produced from the palm oil by using difference of specificgravities and difference of water solubility between "the sulfates andpalm oil. Fatty acids contained in the'palm oil are saponified whileadjusting acid value thereof by adding sodium hydroxide therein, andsodium salts of carboxylic acids thus formed are removed from the palmoil by using the difference of water solubility between the sodium saltsand the palm oil so as to provide reasonably pure fatty acid.

Thus, according to a preferred embodiment of the present invention,there is provided a palm oil recirculation system for cold strip millusing lubricant palm oil together with cooling water and having askimming tank for physically separating used palm oil from water,characterized in that the system comprises an iron removing vessel,which receives the used palm oil from the skimming tank and to whichsulfuric acid is forced together with steam from the cold-strip mill soas to separate iron in the used palm oil as water soluble iron sulfate,which iron removing vessel has a valve selectively discharging the ironsulfates dissolved therein, a saponifying vessel receiving the palm oilfrom the iron removing vessel and caustic soda so as to saponify excessfatty acid in the palm oil into foots, a foots separator removing thefoots by using difference of specific gravities between the foots andpalm oil, and a moisture remover removing moisture from the palm oil soas to ready the palm oil for reuse in the cold-strip mill.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of theinvention, reference is made to the accompanying drawing, in which:

FIG. 1 is a schematic diagram of a system for recirculating palm oil incold-strip mill, according to the present invention;

FIG. 2 is a graph, showing the relation between acid value of the palmoil and the rate at which sulfuric acid is added therein;

FIG. 3 is a graph showing the relation between percent loss of the palmoil and acid value of separated palm oil;

FIG. 4 is a graph showing the relation between concentration of FeO inthe palm oil after being treated by sulfuric acid and the rate at whichsulfuric acid is added therein;

FIG. 5 is a graph showing the variation of acid value of the palm oil asit is heated;

FIG. 6 is a graph showing the variation of the FeO concentration of thepalm oil as it is heated; and 7 FIG. 7 is a graph showing the manner inwhich the concentration of FeO in palm oil varies as it is left tostand.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, when asteel sheet 101 is processed through roll stands 102 in a cold-stripmill, palm oil is injected to a cooperating pair of rolls in each stand102 for lubrication. The lubricant palm oil is collected at an oilcellar 103. Cooling water, which is injected to the roll stands 102, isalso collected at the oil cellar 103, so that the liquid in the oilcellar 103 is a mixture of the used palm oil and the used cooling water.This mixture is brought to a skimming tank 1, so that the comparativelylight palm oil is collected at the top surface of fluid in the skimmingtank 1, which is then led to a scum pit 3 through a suitable conduit.conventionally, the oil collected at the scum pit 3 is discarded orregenerated in a comparatively inefficient manner for reuse in thecold-strip mill. More particularly, when the palm oil from the scum pit3 is directly discarded, it may cause environmental pollution, while thecomparatively inefficient regeneration may cause plugging of theinjection nozzles at the cold-strip mill.

The essential object of the present invention is to mitigate theaforesaid difficulties of conventional process. Furthermore, the presentinvention facilitates recirculation of the palm oil in the cold-stripmill.

After separating the used palm oil, the water from the skimming tank 1has been discarded. Since this water still contains a certain amount ofpalm oil, it is preferable to further purify the water beforedischarging it to the outside of the mill. According to one of preferredembodiments of the present invention, this used water from the skimmingtank 1 is also purified by removing residual palm oil and fatty acidstherefrom.

According to the present invention, the used palm oil, as recollected atthe scum pit 3 is brought to an iron removing vessel 6 for eliminatingiron in the used palm oil. The iron in the used palm oil is in the formof small iron particles and in the form of chemical compounds,- i.e.,iron oxides and iron salt of fatty acid. The used palm oil from the scumpit 3 may be directly delivered to the vessel 6, but the preferredembodiment, as illustrated in FIG. 1, uses a settling tank between thescum pit 3 and the vessel 6, so as to separate solid iron particles andmoisture in the tank 5. A pump 3a is provided for facilitating thedelivery of the used palm oil from the scum pit 3 to the settling tank5.

In the embodiment of FIG. 1, the settling tank 5 acts to separate waterfrom the used palm oil, based on the difference of specific gravitiesbetween them. More particularly, when the used palm oil is left to standin the tank 5 for a certain period of time, the comparatively heavywater gather at the lower portion of the tank 5, while the comparativelylight palm oil gather at the upper portion thereof. A valve 5b is openedto selectively remove water from the tank 5, for delivering the water toa second skimming tank 2 to be described hereinafter. Upon completeremoval of the water, the valve 5b is closed and another valve 50 isopened and a pump 5a is actuated to deliver the used palm oil, whosemoisture has been thus removed, to the settling tank 5.

The used palm oil contains iron in the form of pure iron, iron oxides,and iron salts of fatty acid. The formation of iron salts of fatty acidwill be briefly reviewed. A part of the palm oil is decomposed duringthe lubrication of hydrolysis, of which chemical reaction is given bythe following equation (1).

Hr-O-C 0"R3 Hr-OH R -COOH (palm oil (water) (glycerine) (fatt (1) fat)acid; I

According to the present invention, the iron contained in the used palmoil in the aforesaid forms of free iron, iron oxides, and iron salts offatty acid is turned into water soluble iron sulfates by adding sulfuricacid therein while heating it. To this end, the used palm oil from thescum pit 3, or through the settling tank 5, is delivered into the ironremoving vessel 6, where the used palm oil is mixed with sulfuric acidand heated and agitated by steam from the cold-strip mill. it is a veryimportant factor of the present invention that the heat energy which isnecessary for effecting the aforesaid chemical reaction of convertingthe iron in the used palm oil to the water soluble iron sulfates isprovided by steam which is readily available in the cold-strip mill. Asteam piping l2 delivers such steam. Accordingly, the system of thepresent invention does not require any separate heat source, butexisting steam source in a cold-strip mill can be used for ensuring thecompletion of the chemical reaction of the iron sulfates formation.Furthermore, with the present invention, the steam is simply blown intoa reaction vessel for the iron removing operation. Whereby, both heatingand agitation of the used palm oil can be simultaneously effected bysuch simple blowing of the steam.

The chemical reaction for producing the iron sulfates from the freeiron, iron oxides, and iron salts of fatty acid are as follows.

The iron sulfates thus formed are separated from the palm oil bystanding the mixture of the palm oil and the sulfuric acid in the vessel6, so as to allow the water in the mixture to be accumulated in thelower part of the vessel 6 due to the difference of specific gravitiesbetween the palm oil and water. The water carries the iron sulfates asdissolved therein. Then, a valve 6b is opened, so as to deliver only thewater to a discharge drain tank 19 to be described hereinafter. it isapparent that the iron sulfates are transferred to a water tank 19together with the water. Upon removal of the water, the valve 6b isclosed, and the iron-free palm oil is delivered to a saponifying tank 8by a pump 6a, either directly or through a buffer tank 7.

To ensure satisfactory reactions in the iron removing vessel 6, variousconditions must be properly selected; namely, the rate of addingsulfuric acid in the used palm oil, the reaction temperature in thevessel, heating time, and the duration of standing the liquid in thevessel. The inventors have carefully studied those conditrons.

a. Rate of adding sulfuric acid, and reaction temperature To find outthe proper rate of adding sulfuric acid in the used palm oil, theinventors have carried out tests. Concentrated sulfuric acid with aconcentration of about 98% was added in specimens of the used palm oilwhich consisted of 44% to 60% of palm oil and 40% to 56% of moisture andsludge. The used palm oil with the sulfuric acid was heated at 95 to100C for minutes and left to stand for 4 hours. FIG. 2 shows therelation between the rate of adding sulfuric acid by volume and the acidvalue of the iron-free palm oil to be delivered out of the iron removingvessel 6. The acid value is expressed in terms of mg of potassiumhydroxide which is necessary for neutralizing free fatty acid in theironfree palm oil. When this acid value is too high, the use ful part ofthe palm oil is excessively decomposed into fatty acids, so that theultimate yield of the palm oil is impaired, because once the palm oil isdecomposed into fatty acids it cannot be regenerated easily. Therelation between the yield of the palm oil and the acid value at theoutput of the iron removing tank 6 is shown in FIG. 3. The acid value inthe abscissa of FIG. 3 corresponds to the aforesaid acid value of theiron-free palm oil. The loss, as shown in the ordinate of FIG. 3, is asfollows.

Here,

X: concentration of pure palm oil in the input to the iron removingvessel 6 (g/lit.)

X,: that part of the concentration X which is ultimately delivered froma moisture remover 11 to a palm oil tank 13.

More particularly, when the acid value of the iron-free palm oil fromthe vessel 6 is about 20 mg KOH, the loss is about 11%, namely, about89% of palm oil in the input to the vessel 6 can be recovered andreturned to the palm oil tank 13. The inventors have found out that, tominimize the loss of palm oil forimproving the yield of the regeneratedpalm oil, the rate of adding the concentrated sulfuric acid ispreferably less than 5% by volume. The present invention is notrestricted to such rate of adding sulfuric acid, because the propertiesand conditions of the input palm oil to the iron removing vessel 6varies greatly, depending on how the palm oil is used in the cold-stripmill.

If the aforesaid concentrated sulfuric acid is used, it is preferable toadd more than 1% by volume of the concentrated sulfuric acid in the usedpalm oil, because, for the purpose of iron oxide removal, less than 1%by volume of sulfuric acid is not so effective, as shown in FIG. 4.However, the present invention is not restricted by such minimum rate ofadding sulfuric acid.

The inventors tests also indicated that the preferable temperature inthe iron removing vessel 6 is between 95 and 100C. The removal of ironis, however, possible even outside of such temperature range.

b. Heating time v Tests were made by adding 3% by volume of sulfuricacid into specimens taken from the input to the iron removing vessel 6,heating the mixtures thus prepared for different periods of time,leaving them to stand for 4 hours, and separating the iron-free palm oilfrom the water in the aforesaid manner. FIGS. 5 and 6 show the result ofthe tests; namely, FIG. 5 illustrates the relation between the heatingtime and the acid value of the output iron-free palm oil from the vessel6, while FIG. 6 illustrates the relation between the heating time andthe concentration of FeO in the iron-free palm oil.

As can be seen from FIGS. 5 and 6, in the case of the subject example,the preferable heating time is between 10 minutes to 20 minutes. Suchnumerical example, however, does not restrict the scope of the presentinvention.

c. Standing time Specimens of the used palm oil were allowed to standfor different time periods, after being added with 3% by volume ofsulfuric acid therein and being heated and agitated at to C for 20minutes. After separating iron-carrying water from the palm oil in theaforesaid manner, the concentrations of FeO in the specimens weremeasured. The result is shown in FIG. 7. In this case, the standing timeof 4 hours was sufficient for substantially removing FeO from the palmoil.

Judging from the foregoing equations (1) to (6), the iron-free palm oilfrom the iron removing vessel 6 contains a considerably large amount offatty acids. Therefore, it is necessary to remove the fatty acidtherefrom, so as to provide fairly pure palm oil which is suitable forlubrication in the cold-strip mill. The inventors have found out thatthe removal of the fatty acids can be advantageously effected bysaponifying them by addition of sodium hydroxide therein. In theembodiment, as illustrated in FIG. 1, the iron free palm oil from thevessel 6 is once accumulated in a buffer tank 7, and then forwarded to asaponifying vessel 8 by a pump 7a. The buffer tank 7 is just fortemporary storage, and not essential in the present invention. Thechemical reaction in the saponifying vessel 8 is as follows.

H-O--CQ:R NaOH NaO-COR H 26 (fatty acid) (sodium Y (sodium salt ofhydroxide) carboxylic acid) The rate of adding sodium hydroxide dependson the concentration of fatty acid in the iron-free palm oil. Excesssodium hydroxide spoils the palm oil itself, so that due care must betaken not to excessively add sodium hydroxide. In an embodiment of thepresent invention, the inventors have found out that the addition ofsodium hydroxide in the iron-free palm oil at a rate of 10% and stirringthe mixture thus formed at 60C proved to be satisfactory. This rate ofsodium hydroxide coincides with the amount of it which is theoreticallyrequired for the saponification of the fatty acid in the iron-free palmoil.

The saponified palm oil from the vessel 8 contains sodium salt ofcarboxylic acid, which is generally referred to as foots. To refine thesaponified palm oil, the output from the vessel 8 is forwarded to afoots separator 10 by a pump 8a, either directly or through anothersettling tank 9. The output from the foots separator 10 is forced to amoisture remover 11. The settling tank 9 partly removes the foots fromthe palm oil before forwarding it to the moisture remover 11, but suchsettling tank is not essential in the present invention.

In the foots separator 110, the foots, i.e. sodium salts of carboxylicacid, are dissolved in hot water which is separately forced therein. Thehot water carrying the foots is selectively discharged to the drainwater tank 19 through a valve 10a. After draining the hot water, thepalm oil is forwarded to the moisture remover ll by another pump b. Themoisture remover 11 is, for instance a centrifugal separator or a kindof ion exchanger or any other suitable moisture removing device. so thatmoisture in the palm oil is removed.

The output palm oil from the moisture remover 11 is delivered to an oiltank 13, from which the palm oil is dispatched to injection nozzles forlubricating the roll stands 102 for rolling steel sheets 101. Thus, therecirculation of the palm oil is completed. With the system according tothe present invention, iron contained in the used palm oil, which isinevitable as long as it is used for lubricating the iron rollingprocess at the rolling stands 102, is almost completely removed beforereusing it. Whereby, the 'risk of hardening of the palm oil and pluggingof palm oil injection nozzles can be completely eliminated. in theembodiment of FIG. 1, steam heaters are provided in the settling tank 5,the buffer tank 7, and the palm oil tank 13, for keeping the viscosityof the palm oil in a preferable range.

According to another embodiment, fatty acids contained in the used palmoil is recovered, so as to produce marketable fatty acids. By recoveringfatty acids, the risk of environmental pollution by the fatty acidscontained in the waste water is diminished. At the same time. theeconomy of the palm oil recirculating system for the cold-strip mill isnoticeably improved by the byproducts which are marketable.

Referring to FIG. 1. the residual water from the skiming tank 1 isre-skimmed in another skimming tank 2. The skimming tank 2 also receivespalm oil containing water from the settling tank 5, in case suchsettling tank is used. The palm oil in the skimming tank 2 is collectedby using the difference of specific gravities between the water and thepalm oil. The palm oil is collected in another scum pit 4, while thewater from the skimming tank 2 is forwarded to a waste treating unit.Since the palm oil from the cold-strip mill is skimmed in two stages,the risk of environmental pollution is greatly diminished.

The reused palm oil is forwarded from the scum pit 4 to the dischargeoil tank by a pump 40 and further forwarded to a reaction vessel 21.Residual palm oil and residual saponified fatty acids in the drain watertank 19 are also forwarded to the reaction vessel 21 through the tank20. The reaction vessel 21 also receives sulfuric acid and steam, so asto effect iron separation according to the equations (2) to (6) anddecomposition of sodium salts of carboxylic acid of equation (8) intofatty acids. The iron is selectively removed from the reaction vessel 21by selectively opening and closing a valve 21b, in the same manner asthe valve 6b of the iron removing vessel 6. The output from the vessel21 is forwarded into a decomposing vessel 22 by a pump 21a. Steam andwater are forced into the decomposing vessel 22, so as to carry out thedecomposition of the used or soiled palm oil into fatty acid, accordingto the equation (1). To accelerate the decomposition or hydrolysis, asmall amount of sulfuric acid or other suitable catalyzer may be addedin the vessel 22. Moisture in the decomposing vessel 22 is removed byselectively actuating the valve 22b. After removing the water, themixture of glycerine and fatty acid is forwarded to a temporary storagetank 23 by a pump 22a, and further transferred to a distilling unit 24.After loading a preheating oven of the unit 24 to a proper level, avalve 25a is closed.

The distilling unit 24 includes a burner 34, which heats up thepreheating oven 25, wherein the mixture of the glycerine and fatty acidsis heated, as pointed out above. The preheated mixture is transferred toa distillation still 26 of the unit 24 and a valve 30a is closed. Afterthe contents of the still 26 is heated, a vacuum pressure is appliedthereto from a vacuum pump 28 through a valve 28a, a fatty acid receiver31, a valve 30, a condenser 27, and another valve 30b. Thereby, fattyacid in the distillation still is suddenly evaporated and pulled towardthe condenser 27, where cooling water from piping 28 acts to condensatethe fatty acid. Whereby, liquefied fatty acid is collected in thereceiver 31. After a certain amount of the fatty acid is accumulated inthe receiver 31, the valves 28a and 30c are closed while opening valves30d and 30f, and a pneumatic pressure is applied to the receiver 31 froma compressor 29, so as to transfer the fatty acid to a tank 32. Todeliver the fatty acid from thetank 32, the valves 30d and 30f areclosed and the valve 30e is opened for applying the pneumatic pressureto the tank 32. The residual glycerine from the preheating tank 25 andthe distillation still 26 is drained to a glycerine tank 33, by properlyoperating valves 25b and 26a.

The use of the line for producing the by-product of fatty acids resultsin the following'advantages.

l. The discharge water from the skimming tank 1 is further cleansed forpreventing environmental pollution.

2. The construction and operation of the reaction vessel 21 is similarto those of the iron removing vessel 6, so that the entire system can beconstructed and operated in an economical fashion.

3. Fatty acids produced in the palm oil regenerating process can beeffectively utilized, e.g., for production of grease and soap.

The palm oil which is regenerated from the used palm oil in a cold-stripmill by a system according to the present invention is of high quality,which is comparable with that of fresh palm oil. Physical and chemicalproperties of an example of the regenerated palm oil, which is preparedby the system according to the present invention, is shown in Table l,in comparison with the corresponding properties of fresh palm oil.

' Demulsification was determined by the method of S K 2517.

The specimen of the regenerated palm oil of Table 1 also proved to besubstantially free from fatty acids, which had been a cause of troublesin reusing the lubricant palm oil in the cold-strip mill. Thus, thesystem of the present invention provides an economical way ofrecirculating palm oil in a cold-strip mill, while diminishing the riskof environmental pollution due to direct disposal of used palm oil.

Furthermore, with the present invention, it is also possible to includean optional means for recollecting fatty acid in parallel with theregeneration of the lubricating palm oil. The fatty acid thusrecollected is of such quality that they are marketable for theproduction of grease and soap. Consequently, the construction cost andrunning cost of the overall system for the regeneration andrecirculation of the lubricating palm oil can be minimized.

Although the present invention has been described by referring to apreferred embodiment, it is possible to modify the illustratedembodiment of the system, without departing from the scope of thepresent invention. For instance, the process which is embodied in theillustrated example of recirculating palm oil in a coldstrip mill can bealso applied to recirculation of palm oil in other kind of plant whereinthe palm oil is used as a lubricant together with cooling water. In thelatter case, the palm oil may partly react with a metal with which thepalm oil contacts during the lubrication. The present invention providesa system for separating the metal from the used palm oil containing thecompound between the palm oil and such metal by using a suitable acidwhile heating and agitating the acid-palm oil mixture. In the case ofapplication to a cold-strip mill of steel, the metal is iron and theacid is sulfuric acid.

We claim:

1. A palm oil recirculating system in a plant using lubricant palm oiltogether with cooling water and having a skimming tank for physicallyseparating used palm oil from water, characterized in that the systemcomprises a metal removing vessel, which receives the used palm oil fromthe skimming tank and to which an acid is forced while heating andagitating the metal removing vessel so as to separate metal in the usedpalm oil as water soluble metal sulfate, which metal removing vessel hasa valve selectively discharging water carrying the metal sulfatesdissolved therein, a saponifying vessel receiving the palm oil from themetal removing vessel and caustic soda so as to saponify excess fattyacid in the palm oil into foots, a foots separator removing the foots byusing difference of water solubilities between the foots and palm oil,and a moisture remover removing moisture from the palm oil so as toready the palm oil for reuse in the plant.

2. A palm oil recirculating system for cold-strip mill using lubricantpalm oil together with cooling water and having a skimming tank forphysically separating used palm oil from water, characterized in thatthe system comprises an iron removing vessel, which receives the usedpalm oil from the skimming tank and to which sulfuric acid is forcedtogether with steam from the cold-strip mill so as to separate iron inthe used palm oil as water soluble iron sulfate, which iron removingvessel has a valve selectively discharging water carrying the ironsulfates dissolved therein, a saponifying vessel receiving the palm oilfrom the iron removing vessel and caustic soda so as to saponify excessfatty acid in the palm oil into foots, a foots separator removing thefoots by using difference of hot water solubilities between the footsand palm oil, and a moisture remover removing moisture from the palm oilso as to ready the palm oil for reuse in the cold-strip mill.

3. A palm oil recirculating system according to claim 2, characterizedin that the system further includes a reaction vessel which receivessulfuric acid, steam from the mill, and discharge waters from theskimming tank, the iron removing vessel, the foots separator, and themoisture remover so as to separate iron from the discharge waters aswater soluble iron sulfates while heating and agitating the waters bythe steam, which reaction vessel also decomposes the saponified fattyacids in the discharge waters by the sulfuric acid, which reactionvessel has a valve selectively discharging ironcontaining watertherefrom, a decomposing vessel which receives the output from thereaction vessel and fresh water for decomposing residual palm oil in theoutput from the reaction vessel into glycerine and fatty acids, saiddecomposing vessel having a valve selectively discharging watertherefrom, and a distilling unit which distills the fatty acids from theglycerine.

4. A palm oil recirculating system according to claim 2, characterizedin that a settling tank is disposed be tween the skimming tank and theiron removing vessel, so as to remove water from the used palm oilbefore delivering it to the iron removing vessel.

5. A palm oil recirculating system according to claim 2, characterizedin that another settling tank is disposed between the saponifying vesseland the foots separator, so as to remove water from the output from thesaponifying vessel before delivering it to the foots separator, based onthe difference of water solubilities between the foots and palm oil.

6. A palm oil recirculating system according to claim 2, characterizedin that a temporary storage tank is disposed between the iron removingvessel and the saponifying vessel, so as to continuously feed theiron-free palm oil from the temporary storage tank to the saponifyingvessel.

7. A palm oil recirculating system according to claim 3, characterizedin that another skimming tank is provided between the first skimmingtank and the reaction vessel, so as to further recollect palm oil fromthe discharge water of the first skimming tank.

1. A palm oil recirculating system in a plant using lubricant palm oiltogether with cooling water and having a skimming tank for physicallyseparating used palm oil from water, characterized in that the systemcomprises a metal removing vessel, which receives the used palm oil fromthe skimming tank and to which an acid is forced while heating andagitating the metal removing vessel so as to separate metal in the usedpalm oil as water soluble metal sulfate, which metal removing vessel hasa valve selectively discharging water carrying the metal sulfatesdissolved therein, a saponifying vessel receiving the palm oil from themetal removing vessel and caustic soda so as to saponify excess fattyacid in the palm oil into foots, a foots separator removing the foots byusing difference of water solubilities between the foots and palm oil,and a moisture remover removing moisture from the palm oil so as toready the palm oil for reuse in the plant.
 2. A palm oil recirculatingsystem for cold-strip mill using lubricant palm oil together withcooling water and having a skimming tank for physically separating usedpalm oil from water, characterized in that the system comprises an ironremoving vessel, which receives the used palm oil from the skimming tankand to which sulfuric acid is forced together with steam from thecold-strip mill so as to separate iron in the used palm oil as watersoluble iron sulfate, which iron removing vessel has a valve selectivelydischarging water carrying the iron sulfates dissolved therein, asaponifying vessel receiving the palm oil from the iron removing vesseland caustic soda so as to saponify excess fatty acid in the palm oilinto foots, a foots separator removing the foots by using difference ofhot water solubilities between the foots and palm oil, and a moistureremover removing moisture from the palm oil so as to ready the palm oilfor reuse in the cold-strip mill.
 3. A palm oil recirculating systemaccording to claim 2, characterized in that the system further includesa reaction vessel which receives sulfuric acid, steam from the mill, anddischarge waters from the skimming tank, the iron removing vessel, thefoots separator, and the moisture remover so as to separate iron fromthe discharge waters as water soluble iron sulfates while heating andagitating the waters by the steam, which reaction vessel also decomposesthe saponified fatty acids in the discharge waters by the sulfuric acid,which reaction vessel has a valve selectively dischargingiron-containing water therefrom, a decomposing vessel which receives theoutput from the reaction vessel and fresh water for decomposing residualpalm oil in the output from the reaction vessel into glycerine and fattyacids, said decomposing vessel having a valve selectively dischargingwater therefrom, and a distilling unit which distills the fatty acidsfrom the glycerine.
 4. A palm oil recirculating system according toclaim 2, characterized in that a settling tank is disposed between theskimming tank and the iron removing vessel, so as to remove water fromthe used palm oil before delivering it to the iron removing vessel.
 5. Apalm oil recirculating system according to claim 2, characterized inthat another settling tank is disposed between the saponifying vesseland the foots separator, so as to remove water from the output from thesaponifying vessel before delivering it to the foots separator, based onthe difference of water solubilities between the foots and palm oil. 6.A palm oil recirculating system accorDing to claim 2, characterized inthat a temporary storage tank is disposed between the iron removingvessel and the saponifying vessel, so as to continuously feed theiron-free palm oil from the temporary storage tank to the saponifyingvessel.
 7. A palm oil recirculating system according to claim 3,characterized in that another skimming tank is provided between thefirst skimming tank and the reaction vessel, so as to further recollectpalm oil from the discharge water of the first skimming tank.